1. Field of the Invention
The present invention relates to a method for manufacturing electronic components of laminated ceramics such as laminated ceramic capacitors, laminated inductors, multi-layer circuit boards and laminated piezoelectric members. The present invention particularly relates to a method for manufacturing electronic components of laminated ceramics comprising the processes of laminating a plurality of ceramic green sheets on which films of inner circuit elements such as conductive films having a given thickness are partially formed.
2. Description of the Related Art
A plurality of ceramic green sheets are prepared and laminated for manufacturing electronic components of laminated ceramics such as laminated ceramic capacitors. Films of inner circuit elements such as conductor films and resistor films for constructing capacitors, resistors, inductors, varistors and filters are formed on a specified green sheet depending on the desired functions of the electronic component of laminated ceramics.
Thin layer and multi-layer ceramic green sheets have been developed in order to make the electronic component of laminated ceramics have a small size and have high performance. For example, the laminated ceramic capacitor may be small size while having a large capacitance by laminating a plurality of the thin ceramic green sheets. However, the thickness of the film of inner circuit elements greatly influences the performance of the ceramic components as the green sheet is made thinner and larger numbers of the ceramic green sheets are laminated, causing the following problems.
Step heights are accumulated by the difference of thickness between the portions where the film of inner circuit elements is formed and not formed, when the film of inner circuit elements is formed on the ceramic green sheets followed by laminating the sheets. Therefore, the pressure used to press the laminate obtained by laminating the ceramic green sheet is not uniformly applied along the direction of the principal faces of the ceramic green sheets, sometimes causing delamination of the laminate. Otherwise, the surface of the laminate partially expands to form non-plane surface that generates cracks in the firing process thereafter.
For solving these and other problems, it is proposed to eliminate the steps on the ceramic green sheets by applying the ceramic paste by screen printing, photogravure printing or relief printing on the area of the ceramic green sheet where no films of inner circuit elements are formed.
The method for manufacturing the ceramic capacitor will be described in more detail with reference to FIG. 1. Ceramic green sheets 1a and 1b are prepared at first as shown by the processes (1A) and (1B) in FIG. 1.
Inner electrodes 2a and 2b as films of inner circuit elements are formed on the principal faces of the ceramic green sheets 1a and 1b as shown by the processes (2A) and (2B) in FIG. 1. These inner electrodes 2a and 2b have given thicknesses, respectively, thereby steps 3a and 3b appear due to the thickness of each film.
In the process for forming the inner electrode 13 (FIG. 4B), the inner electrodes 2a and 2b are formed so as to merely reach one terminal edge along the longitudinal direction located at the end along the longitudinal direction of respective rectangular principal faces of the ceramic green sheets 1a and 1b, and not to reach the two terminal edges located at the ends along the transverse direction and the other terminal edges located at the end along the longitudinal direction.
As shown by the processes (3A) and (3B) in FIG. 1, ceramic pastes 4a and 4b are applied by screen printing, photogravure printing or relief printing on the area of the principal faces of the ceramic green sheets 1a and 1b where no inner electrodes 2a and 2b are formed, thus substantially eliminating the steps 3a and 3b due to the inner electrodes 2a and 2b as shown by the processes (2A) and (2B) in FIG. 1.
The ceramic pastes 4a and 4b should have a viscosity of given value or more for maintaining resolution of the ceramic pastes 4a and 4b applied by printing higher than a prescribed level in the printing processes of the ceramic pastes 4a and 4b . Accordingly, the content of solvents in the ceramic pastes 4a and 4b is usually adjusted to 35% by weight or less.
The ceramic green sheets 1a and 1b shown by the processes (3A) and (3B) in FIG. 1, respectively, are alternately laminated. This means that the terminal edges at the ends along the longitudinal direction where the inner electrode 2a or 2b reach, and the terminal edges at the ends along the longitudinal direction where the inner electrode 2a or 2b do not reach, are alternately arranged along the direction of lamination. A laminate 5 as shown by the process (4) in FIG. 1 is obtained by laminating the ceramic green sheets 1a and 1b. 
The laminate 5 is fired after pressing. A desired laminated ceramic capacitor is completed by forming auxiliary circuits at both ends of the laminate 5.
Since the steps 3a and 3b due to the thicknesses of the inner electrodes 2a and 2b can be substantially eliminated by the methods as described above, the ceramic green sheets 1a and 1b can be laminated without being substantially affected by the thicknesses of the ceramic green sheets 1a and 1b. Accordingly, the thin ceramic green sheets 1a and 1b can be laminated while allowing delamination and cracks in the laminate 5 to be scarcely generated.
A method for obtaining one laminate 5 is illustrated in FIG. 1. However, each process shown in FIG. 1 is usually carried out so as to manufacture a mother laminate for yielding a number of laminates 5, in order to efficiently obtain a plurality of laminates 5. The mother laminate is cut to isolate individual laminates 5 from it by executing each process shown in FIG. 1. For this purpose, each ceramic green sheet 1a and 1b shown in FIG. 1 is prepared as a mother sheet having a large dimension. The inner electrodes 2a and 2b are formed, and the ceramic pastes 4a and 4b are applied on this mother sheet, followed by laminating the mother green sheets.
However, the method for eliminating the steps on the ceramic green sheets as hitherto proposed involves the following problems.
FIG. 2 shows an extended cross section of a part of the ceramic green sheet 1 as a mother sheet, and a part of the inner electrode 2 formed on the principal face of the green sheet as described above. The ceramic paste 4 inadequately applied on the principal face of the ceramic green sheet 1 is also illustrated, although the object of applying the ceramic paste has been to substantially eliminate the steps due to the thickness of the inner electrode 2.
While the ceramic paste 4 is applied by screen printing, photogravure printing or relief printing as described above, the positional accuracy of these printing methods is about 30 to 200 xcexcm. Consequently, a part of the ceramic paste 4 overflows on the inner electrode 2 when the printing position has shifted, thereby enhancing the step rather than demising it.
For avoiding the foregoing problems from occurring, it is proposed to designed the printing pattern of the ceramic paste 4 so as to form a gap 6 (FIG. 3) with a space of, for example, several tens microns between the ceramic paste 4 and the inner electrode 2, thereby allowing the ceramic paste 4 to hardly overflow on the inner electrode 2 even when the printing position has been a little shifted. However, this method also involves some problems that the terminal edge of the inner electrode 2 is apt to be distorted by the presence of the gap 6, or that structural defects such as voids are liable to be generated in the laminate after firing.
Accordingly, the object of the present invention is to provide a method for manufacturing an electronic component of laminated ceramics that is able to solve the problems as hitherto described. In a first aspect, the present invention provides a method for manufacturing an electronic component of laminated ceramics comprising the processes of:
preparing a ceramic green sheet; partially forming a film of inner circuit elements on the principal face of the ceramic green sheet while forming steps corresponding to the thickness of the film; applying a ceramic paste on the principal face of the ceramic green sheet so that steps due to the thickness of the film of the inner circuit elements are substantially eliminated; and laminating the ceramic green sheets on which the ceramic paste has been applied.
In the first aspect for solving the technical problems as hitherto described, the film of inner circuit elements is formed at the periphery of the film to give an inclined face with an acute angle against the principal face of the ceramic green sheet in the process for forming the film of inner circuit elements, and the ceramic paste is applied so as to overlap the periphery of the film of inner circuit elements in the step for forming the film of inner circuit elements.
In the second aspect, the ceramic paste is also coated so as to overlap the periphery of the film of inner circuit elements in the process for coating the ceramic paste, a ceramic paste containing about 40% by weight to 85% by weight of a solvent being used as the ceramic paste.
The method for manufacturing the electronic component of laminated ceramics in the third aspect of the present invention may comprise the features of the first and second aspects. The film of inner circuit elements is formed at the periphery of the film to give an inclined face with an acute angle against the principal face of the ceramic green sheet in the process for forming the film of inner circuit elements, and the ceramic paste is applied so as to overlap the periphery of the film of inner circuit elements, wherein a ceramic paste containing about 40% by weight to 85% by weight of a solvent is used as the ceramic paste.
The inclined face is preferably formed so as to have an angle of about 0.3 degree to about 30 degrees against the principal face of the ceramic green sheet in the first or third aspect of the present invention.
The ceramic paste is applied so as to overlap the periphery of the film of inner circuit elements with an overlap width of up to about 180 xcexcm, preferably with an overlap width of about 20 to 140 xcexcm, in the first to third aspect of the present invention.
Although the ceramic paste containing about 40% by weight to 85% by weight of a solvent is used in the second and third aspects of the present invention, it is also preferable to use the ceramic paste containing about 40% by weight to 75% by weight of the solvent in the first to third aspects of the present invention.
The present invention can be advantageously applied particularly to the method for manufacturing a laminated ceramic capacitor. The ceramic green sheet has a rectangular principal face when individual ceramic capacitor to be manufactured is a unit capacitor. In the process for forming the film of inner circuit elements that serves as an internal electrode for ensuring an electrostatic capacitance, the film of inner circuit elements is formed so as to merely reach one terminal edge along the longitudinal direction located at the longitudinal end of the rectangular face of the ceramic green sheet while being formed so as not to reach two terminal edges along the transverse direction located at the other terminal edge along the longitudinal direction and at the end along the transverse direction, respectively. A plurality of the ceramic green sheets are laminated so that the terminal edge along the longitudinal direction where the film of inner circuit elements reaches and the terminal edge along the longitudinal direction where the film of inner circuit elements does not reach are alternately arranged along the direction of lamination.
While the ceramic paste is coated on the entire area on the principal face of the ceramic green sheet where the film of inner circuit elements is not formed in the process for coating the ceramic paste, the ceramic paste may be merely coated on the area sandwiched between the terminal edge along the transverse direction of the principal face and the film of inner circuit element on the ceramic green sheet when the present invention is applied to the method for manufacturing the laminated ceramic capacitor.